1. Field of the Invention
The present invention relates to an electrical connector connecting to a printed circuit board (PCB) by solder balls, especially to a ball grid array (BGA) socket having attached with a solder ball capable of providing extension so as to compensate warpage of the socket thereby ensuring reliable soldering with respect to solder pads on a printed circuit board.
2. Description of Related Art
As FIG. 1 shown, a conventional solder ball 10 contains a ball-shaped core portion 20 and a layer 30 of alloy solder coated an outer periphery of the core portion 20. The core portion is made from an alloy of tin (Sn) and other metal, such as SnPb, SnAg, SnAgCu. The core portion also can adopt copper(Cu) material for forming a high solder temperature. Said alloy core portion and copper core portion have a same high rigidity capability, which does not attract momentary stress when exterior force is exerted thereon. As a result, the stress is directly exerted on the soldering interface of the solder balls and the PCB and the soldering interface will rupture. And more, the alloy core portion will produce an inter-metallic compound (IMC) thereinside after a long and high temperature, and grains of IMC will enlarged resulting intensity descend of the solder ball. As a result, the solder ball will crack along the IMC during endure thermal fatigue stress.
Furthermore, the solder ball will bring out more disadvantage if it is copper cored solder ball. FIG. 1 shows the rupturing process when the solder ball has a copper core portion 20. When the electrical connector 40 is connecting with the PCB 70 in a solder reflow oven during SMT process, the insulating housing 50 of the connector is distorted upwards but the solder ball 10 remains as original ball since the copper core portion 20 has a higher temperature than the periphery temperature. So the solder joint of the solder balls and the PCB will disconnect.
Therefore, an improved solder ball is desired to overcome the disadvantages of the prior arts.